Most endless power transmission belts of trapezoidal cross-sectional outline, or so-called V-belts, in current use are made with a load-carrying section which is arranged closer to the wider parallel side of the trapezoidal cross section because heretofore such arrangement has proven superior in many respects. However, many of such currently used V-belts are inherently comparatively expensive because there is considerable scrap produced when cutting such V-belts from the usual cylindrical sleeve produced by many well-known techniques.
To reduce the cost of V-belts by reducing scrap, proposals have been made heretofore to cut the usual cylindrical sleeve in what is often referred to as a balanced manner. Examples of this are shown in U.S. Pat. Nos. 1,432,973; 1,924,355; 2,153,966; and 2,661,045.
It is also well known to provide belts of substantially trapezoidal cross-sectional configuration having a load-carrying section or so-called neutral axis which is located centrally, as shown, for example, in two of the above mentioned U.S. Pat. Nos. 1,924,355 and 2,661,045. U.S. Pat. No. 2,661,045 further teaches the provision of at least one fabric reinforcing layer on each side of the tension member to provide high compressive and tensile moduli in the transverse direction of the belt. However, belts of the type disclosed in these two patents are comparatively expensive to produce.
A V-belt which, in essence, uses the prior art features of the above-mentioned patents is disclosed in U.S. Pat. No. 3,869,933 and it is stated that the belt of this latter mentioned patent may also use fiber-loaded elastomeric material as disclosed in U.S. Pat. No. 3,416,383. However, in FIG. 5 of U.S. Pat. No. 3,869,933 and the associated description in the specification emphasize that a belt having a central load-carrying section and made with fiber-loaded material and layers of stretchable fabric to define its top and bottom surfaces loses its transverse stiffness and sags. Accordingly, great emphasis is given in U.S. Pat. No. 3,869,933 to the use of so-called fabric reinforcing layers which have high compressive and tensile moduli to provide transverse rigidity; however, it is well known that fabric reinforcing layers used in the manner disclosed in this last mentioned patent result in sharply defined shear planes which cause a belt made in this manner to delaminate after a comparatively short service life.
In any event, any V-belt which requires a large number of different layers with each different layer being required to impart a special desired characteristic to the V-belt usually results in adding to the cost of such belt.
Recently, the automobile industry has shown considerable interest in balanced cut V-belts with centrally located load-carrying sections because of the potential cost savings, due to reduced scrap alone, in producing such belts as compared with the usual belts having eccentric load-carrying sections. However, it is a problem to provide such a balanced cut belt with a central neutral axis at minimum cost yet assure the belt is capable of being reliably operated at high speeds over a plurality of small diameter sheaves of the type used on accessories of an automobile engine, for example, for an extended service life.